This invention relates to containers having a pre-formed opening or pour hole therein covered by a removable (i.e. hand peelable) closure system. The invention also relates to end portions useful for containers adapted to package carbonated beverages.
Over the past several years there has been increasing usage of metal containers for carbonated beverages such as soft drinks and beer. The most common of these metal containers employ an easy open closure in which a metal ring attached to the end wall is lifted and pulled away in order to remove a portion of the end wall along weakened tear lines. However, such closure systems are becoming very ecologically unacceptable because the removed metal tabs, which are commonly discarded on the ground or in lakes, etc., decompose only very slowly and, due to their sharp edges, are quite dangerous in areas such as beaches where people walk barefoot.
Although it is known that unpressurized cans containing tomato juice and similar liquids can be provided with easy open closures comprising pressure sensitive adhesive tape tabs (e.g. as disclosed in U.S Pat. No. 3,389,827), such closure systems have not been acceptable for use in connection with containers in which are packaged gas-containing liquids (e.g. carbonated soft drinks and beer). Typical gas pressures for various beverages at 38.degree. C. are as follows: orange pop, 1.7 kg/cm.sup.2 ; strong beer, 3.3 kg/cm.sup.2, root beer, ginger ale, cola, lemon, 4.5 kg/cm.sup.2 ; club soda, 5.8 kg/cm.sup.2. At room temperature the gas pressures are about 70% of these, and even under normal refrigeration (e.g. 4.degree.-5.degree. C.) the gas pressures are about 40% of those stated. Such gas pressures ordinarily cause prior art tape closures to bulge upward and gradually peel away from the area immediately circumjacent to the pre-formed opening (i.e. pour hole) whereby the can seal is broken.
Although U.S. Pat. Nos. 2,870,935, 3,292,828, and 3,339,788 purport to describe various easy open closure systems useful in conjunction with containers containing carbonated beverages, such systems have had only limited commercial success. A major problem encountered in the development of such closures is the difficulty of obtaining materials which have sufficient physical properties to be formed into such a seal under the conditions encountered in the filling and closing of metal containers. Furthermore, the disclosures in such patents regarding the materials which may be satisfactory for use are very general and do not provide a basis for discriminating between materials which are suitable for use in the system and those which are not.
In accordance with the present invention it has been found that of the myriads of available starting materials (in terms of films, adhesives, etc.) there are limited and select materials which are suitable in making closure systems having the proper balance of many characteristics necessary in order to be commercially acceptable.